An American university student is free after being detained for a week in China for allegedly injuring a taxi driver who manhandled his mother during a fare dispute, in a case that brought U.S. lawmakers to the student's defense.

Guthrie McLean, a University of Montana student, was released from a Zhengzhou detention center early Monday, according to his mother, Jennifer McLean, a teacher who lives in the central Chinese city.

"We are very, very, very, very happy," Jennifer McLean wrote in an email to The Associated Press. She said the release — at 2 a.m. local time, when her son was delivered to her doorstep — came as a surprise after she was twice told to anticipate his release only to be disappointed.

"They have not finished the process completely, but we are hopeful it will go smoothly from here on," Jennifer McLean said.

The U.S. State Department confirmed Guthrie McClean's release but provided no details, citing privacy concerns.

"The safety and security of U.S. citizens overseas is one of the Department's highest priorities," it said in a statement.

Guthrie Mclean's release followed an agreement with Chinese authorities to drop any charges against him, according to Montana U.S. Sen. Steve Daines. Details on the deal were not disclosed.

Daines and Montana's other congressional delegates — U.S. Sen. Jon Tester and Rep. Greg Gianforte — had pressed McLean's case with China's ambassador to the U.S., Cui Tiankai, and U.S. Secretary of State Rex Tillerson.

The lawmakers said Guthrie McLean had justifiably defended his mother, who is deaf, from the driver, whose knee was reportedly hurt in the encounter.

Jennifer McLean told the AP the taxi driver was shoving her and hurting her when her son intervened and pushed the taxi driver to the ground.

Jennifer McLean said that when police detained her son five weeks later on charges of intentional injury, they demanded the equivalent of $7,400 in compensation and threatened to imprison him for up to three years if they refused to pay.

People who answered the phones at Zhengzhou police headquarters said there was no one available to comment on the case.

The family did not pay $7,400, according to Daines, who added that more details would be released at a later time.

``After two 20-hour days in back and forth negotiations with Chinese officials, we were able to come to an agreement that worked for everybody, most importantly for Guthrie and for Jennifer,'' Daines said in a conference call with reporters.

Daines said he spoke with Guthrie McLean after his release, and he plans to return to Montana to resume his studies next month.

Tester and Gianforte issued statements Sunday saying they were pleased with the outcome.

Guthrie McLean has been majoring in East Asian studies at the University of Montana in Missoula for about two years and works in the Department of Modern and Classical Languages and Literatures, according to school officials.

He is a U.S. citizen but he largely grew up in China after living in Missoula as a young child while his mother was studying at the university, according to his boss, Olivia White.